International observers in Venezuela say an audit of the referendum results which confirmed President Hugo Chavez's mandate in office has revealed no evidence of fraud.

It is the third time in a week that foreign monitors have endorsed the outcome after opponents of Mr Chavez's rule alleged that electronic voting machines were rigged.

Jennifer McCoy of the Carter Centre, an independent observer group headed by the former US president, Jimmy Carter, said that careful checks had revealed no discrepancies.

However, Mr Chavez's opponents reject the result and demand a blanket audit of all voting machines.